Double exceptional points in grating coupled metal-insulator-metal heterostructure

Area of Science:

• * Photonics and Nanotechnology
• * Non-Hermitian Systems
• * Metamaterials

Background:

• * Metal-insulator-metal (MIM) heterostructures offer unique optical properties.
• * Non-Hermitian systems exhibit complex behaviors like exceptional points (EPs).
• * Grating coupling can control light-matter interactions in nanostructures.

Purpose of the Study:

• * To theoretically investigate exceptional points and reflection spectra in grating-coupled MIM heterostructures.
• * To explore the role of geometrical parameters, particularly grating periodicity and metal layer thickness, on system behavior.
• * To demonstrate the potential for achieving unidirectional reflectionless propagation (unidirectional invisibility) and asymmetric transmission.

Main Methods:

• * Theoretical analysis of a non-Hermitian MIM heterostructure model.
• * Numerical simulations to study the effects of grating periodicity and layer thickness.
• * Analysis of reflection and transmission spectra under varying conditions.

Main Results:

• * Double exceptional points observed at specific grating periodicities (~150 nm) under zero reflection conditions.
• * Partition metal layer thickness controls mode coupling and splitting, influencing reflection properties.
• * Unidirectional invisibility achieved via vanishing reflection; asymmetric transmission demonstrated for larger grating periodicities (≥400 nm) due to diffraction.

Conclusions:

• * The study provides a theoretical basis for designing coupled non-Hermitian photonic systems with double EPs and asymmetric transmission.
• * The proposed heterostructure is a promising candidate for next-generation optical communications, sensing, photo-detection, and nano-photonic devices.